1. Field of the Invention
This invention relates to a micromanipulator adapted for use in fields requiring precise positioning on the .mu.m order, particularly for use in the integrated circuit (IC) industry (for precision wafer positioning), bioengineering, medicine (microsurgery), satellite communications (precise antenna positioning) etc.
2.Description of the Prior Art
Micromanipulation is the technology of conducting operations on minute objects (for example, cells) with sizes on the order of several tens of .mu.m. It can be effectively applied, for instance, for grasping a minute object with two fingers and positioning it by translational and rotational motion, as well as for operations such as gripping, pressing, cutting, stretching, compressing, perforating, mixing and propelling. As such, it has become an indispensable technology in a wide range of fields including biotechnology and medicine. However, since most of the micromanipulators that have become commercially, available up to the present consist of a combination of a mechanism for translational motion in three mutually perpendicular directions and a gripper, they are not optimally adapted for use with microscopic objects.
In view of these circumstances and in light of the fact that in the microworld surface forces are dominant over inertial force, the inventor concluded that a two-finger microhand would be capable of sufficiently stable micromanipulation. He therefore developed a two-finger hand with a drive mechanism utilizing parallel linkages with six degrees of freedom (DOF). This micromanipulator, which is described in Japanese Patent Application Hei 3(1991)-305,220, was confirmed to be highly effective as regards operability, controllability and the like.
This earlier proposed micromanipulator is constituted as a two-finger hand employing a pair of hand modules with 6-DOF parallel linkages. Each hand module has a base plate and an end-effector consisting of a moving plate and a finger attached to the moving plate. The base plate and the moving plate are connected by six links that are extended and contracted by piezoelectric actuators. The six links are divided into two groups of three each. The links of both groups are connected with the base plate and the moving plate at points spaced along circles whose centers are the axial centers of the plates, but the links of one group are inclined in the opposite direction from those of the other group. Since the need for the micromanipulator to be compact makes it difficult to use ball joints or the like for connecting the links with the base plate and the moving plate, the connection is made by pivots and springs connected between the base plate and the moving plate for retaining the links in a squeezed state between the base and moving plates.
Although this configuration is highly effective from the viewpoint of reducing the size of the micromanipulator, various tests conducted on a prototype configured in line with this design revealed shortcomings. First, since the links are held between the base plate and the moving plate of the end-effector by spring force, the micromanipulator is liable to break down structurally when exposed to an external force exceeding the spring force. Second, since the springs constitute a vibration system, the micromanipulator cannot be used in the natural frequency range of the vibration system determined by the spring constant and the mass of the vibrating members and is further unable to follow rapid movements with adequate response. From the test results it was concluded that configurational improvements for coping with these problems would enable realization of a practical micromanipulator.
The present invention was achieved in light of the foregoing findings and has as its object to provide a micromanipulator which is strong enough not to structurally break down easily under external force and which, not having a spring vibration system, is able to follow rapid movements with good response.